You can do this in an ActiveX Script like below...
Function Main()
Dim myYearQtr
myYearQtr = InputBox ("Enter the date you would like to extract data for.", "Extract Data","4Q2003")
DTSGlobalVariables("myYearQtr").Value = myYearQtr
Main = DTSTaskExecResult_Success
End Function
You can then use the global variable that is set anywhere in the DTS.